Among the close on 40,000 runners pounding the capital's streets today are dozens supporting Jewish charities, many with poignant reasons for taking part.
Jewish Care's contingent includes Lauren Waterman, 26, who is running in memory of her grandma Barbara Waterman, who died last year aged 84. Barbara was a Jewish Care volunteer for virtually half-a-century and her granddaughter is raising funds for the Brenner Centre at Stepney Jewish Community Centre where Mrs Waterman was so heavily involved, "making it her mission to support the community and put a smile on members' faces".
Running for Norwood is Adam Waters, 28, honouring the memory of his late grandfather Dennis Temple, who grew up in the charity's former orphanage and served with the RAF in the Second World War.
Mr Waters, 28, said his grandfather “always spoke fondly” about his time at the orphanage.
“He made great friends there, and got up to many high jinks. He once snuck out of the orphanage to go and see a film he had particularly wanted to see. When he arrived back later that day - very relieved he hadn't been caught - the orphanage announced they were taking the boys on an outing for a special treat to the pictures to see the exact film he had just watched.”
Camp Simcha supporter Marc Cohen is going the extra mile for the charity - 26 in fact. Having completed last week's Manchester Marathon, the 31-year-old is doubling up in London to thank the charity for supporting his four-year-old nephew Jake, who is receiving treatment for neuroblastoma, a cancer that forms in certain types of nerve tissue.
“I wanted to do something for Camp Simcha as they have been incredible to my family," Mr Cohen said. "I decided to do the double marathon to raise extra money.”
For Emunah runner Dan Brazil, the motivation was somewhat different. Holidaying in Israel last summer, he couldn’t fit into his swimming trunks and so decided he needed to lose weight and get fit. Now some four stones lighter, he gets up at the crack of dawn each day to go running.